It is often desirable to provide visual information to a living being, usually a person. Frequently one wishes to superimpose such visual information upon the being's view of the real world.
Such a display requires, in a form known as a folded catadioptric display, an image generator; a beam splitter, which receives the image light from the image generator and sends a fraction, designated the reflected fraction, of such image light to a reflective combiner that both allows light from the real world to pass through such combiner and reflects the image light such that both the real-world light and the image light are transmitted to the eye of the user through the beam splitter.
The beam splitter will transmit a fraction, designated the transmitted fraction, of the image light reflected from the collimator-combiner. Of course, only a fraction of the real-world light is also transmitted by the beam splitter.
To correct for aberrations and distortions produced by the beam splitter and the combiner, a correction lens is often placed in the optical path between the image generator and the beam splitter.
Another beneficial process in a visual display is depixelation of the image.
The image generators that are well known in the art, such as a cathode ray tube and a liquid crystal display, produce an image composed of a multiplicity of pixels. Each pixel is a point of light. Since adjacent pixels do not contact each other, every pixel is surrounded by a dark area. The combiner magnifies the image, causing the dark area to be perceptible and thereby detracting from the accurate portrayal of the image one wishes to depict.
Depixelation traditionally comprises blurring the edges of the pixels without losing resolution or contrast. In fact, perceived resolution--although necessarily somewhat subjective--appears to be increased by depixelation. And, in the case of triads of colored pixels, depixelation blends the colors together.
In U.S. application Ser. No. 07/832,237, the inventor achieves depixelation of a liquid crystal display through the placement of a fiber optic faceplate between the liquid crystal display and the beam splitter, a fold mirror in that case, in such a manner that the input numerical aperture of the faceplate is approximately equal to twice the pixel size of the liquid crystal display divided by the distance between the fiber optic faceplate and the pixels.
A second process for achieving depixelation with a fiber optic faceplate involves simply placing the source of light for the liquid crystal display near the rear of the pixel plane of the liquid crystal display. Since the input surface of the faceplate is a finite distance in front of the pixel plane of the liquid crystal display, the image of each pixel on the input surface of the faceplate is not only enlarged, but also covers a greater portion of the total picture, correspondingly decreasing the amount of dark area surrounding each pixel. Also, the small size of each pixel causes considerable diffraction of the light which passes the edge of the pixel.
A common and third technique for depixelation is locating a weak diffuser plate a short distance from the pixels, in the direction of the beam splitter.